| Year | Value | | 2022 | 2.8350279864446 | | 2021 | 0.58181416848986 | | 2020 | 0.72587493331338 | | 2019 | 0.36288617994061 | | 2018 | 0.93633546411356 | | 2017 | 0.5337878398259 | | 2016 | 0.43461866428584 | | 2015 | -1.1439086722818 | | 2014 | 0.013202538751494 | | 2013 | 0.21732315511569 | | 2012 | 0.69255201810525 | | 2011 | 0.2313492076509 | | 2010 | 0.68823870722003 | | 2009 | 0.48048193642328 | | 2008 | 2.4260411706016 | | 2007 | 0.73235060312225 | | 2006 | 1.059509283248 | | 2005 | 1.171954203337 | | 2004 | 0.80290873095523 | | 2003 | 0.6382729308872 | | 2002 | 0.64271150654328 | | 2001 | 0.98902032983255 | | 2000 | 1.5585291967901 | | 1999 | 0.80644438095945 | | 1998 | 0.01793843784391 | | 1997 | 0.52022542273665 | | 1996 | 0.81163406462821 | | 1995 | 1.7998277686714 | | 1994 | 0.8521169951207 | | 1993 | 3.2926218031361 | | 1992 | 4.0370302077874 | | 1991 | 5.8595966346867 | | 1990 | 5.4039590921894 | | 1989 | 3.1552697971091 | | 1988 | 1.8724685973187 | | 1987 | 1.4403218804172 | | 1986 | 0.75030983941078 | | 1985 | 3.4353993529827 | | 1984 | 2.9314566913662 | | 1983 | 2.9497944354572 | | 1982 | 5.6551018239234 | | 1981 | 6.4903096400572 | | 1980 | 4.02250084839 | | 1979 | 3.6476401055879 | | 1978 | 1.0287928948742 | | 1977 | 1.2959991627832 | | 1976 | 1.7154763228565 | | 1975 | 6.6965952250783 | | 1974 | 9.7674143191302 | | 1973 | 8.7546703302464 | | 1972 | 6.6600070416024 | | 1971 | 6.573221119258 | | 1970 | 3.6159867862952 | | 1969 | 2.4890359895938 | | 1968 | 2.3958222695702 | | 1967 | 4.0051962156387 | | 1966 | 4.775979595637 | | 1965 | 3.4144786084618 | | 1964 | 3.0805568710181 | | 1963 | 3.4402128804295 | | 1962 | 4.3159928775439 | | 1961 | 1.8453978744866 | | 1960 | 1.4387947032109 |
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